1. Field of the Invention
The present invention relates to a method for cutting a multiplicity of disks from a hard brittle workpiece with the aid of a wire saw. The invention also relates to a wire saw which is suitable for carrying out the method. The invention can be used for all hard brittle materials which are to be sawn into wafers, in particular semiconductor material and ceramics. The invention is particularly suitable for cutting off silicon wafers from a single crystal.
2. The Prior Art
Currently, wire saws which operate with a cutting slurry are predominantly used to produce silicon wafers. In these saws, a steel wire with a length of 50 km to 500 km runs helically over wire-guidance rollers and forms a wire web. Generally, a hard material, for example SiC, in a carrier liquid is used as the cutting lapping medium. It is supplied during the cutting operation and is transported freely into the cutting gap by the movement of the wire. In the process, depending on the cutting length and feed path, several hundred wafers are produced simultaneously in a process which lasts several hours. The sawing wire is either moved in the same direction throughout the entire cutting sequence or is moved back and forth (oscillating wire movement). When moving with a directional change, the forward movement is always longer than the backward movement, with the result that as yet unused sawing wire is also constantly being deployed.
The prior art also encompasses single-wire cutting methods in which the sawing wire is covered with bonded abrasive grain and makes only a single incision into the workpiece. It is possible to differentiate between methods in which a wire loop (endless, constant direction of movement) is used and methods in which an endless sawing wire with oscillating wire movement is used. In the case of the oscillating methods, the sawing wire is unwound from a spool, runs to the workpiece and is wound back onto a receiving spool.
The present invention relates to a method for cutting a multiplicity of disks from a hard brittle workpiece, by moving the workpiece at a defined feed rate through a wire web of a wire saw, wherein the wire web is formed by a sawing wire which moves in a reciprocating manner and is covered with bonded abrasive grain, and a cooling liquid is provided beneath the wire web, in which liquid the sawing wire of the wire web is immersed when cutting off the disks.
The invention makes it possible to cut off wafers without the expensive operations of supplying and disposing of slurry, and the associated high outlay on equipment, together with the ecological problems which have to be taken into consideration. It utilizes the fact that bonded grains or particles have an abrasive action and therefore cut more efficiently than the hard materials in a slurry, which have a lapping action. The invention makes it possible in particular to achieve higher cutting capacities, shorter process times and improved cutting qualities. In addition, the method of the invention does not exhibit the drawbacks of known single-wire cutting methods, which are uneconomical, since it is only possible to produce one disk each time. An additional drawback of the prior art is that the cutting times are very long compared to competitor methods for making single cuts, such as annular sawing.